1. Field of the Invention
The present invention relates to a platinum electroforming and also to a platinum electroplating.
Platinum has widely been used as ornaments or accessories because of its clean and subdued shine, although it has a less loud color than gold. Platinum is also highly resistant to corrosion and gives a catalytic effect, and thus it can be adopted as materials for products used in industries.
Platinum, however, has an inherent tenacity, which brings about a decreased workability of platinum. A high degree of technical skill of a professional workman is imperative especially for the working of accessories such as earrings or brooches which requires elaborate workmanship for the manufacture.
Furthermore, inasmuch as the specific gravity of platinum is higher, for example, than that of white gold made of an alloy of gold and silver, it cannot be made into large-sized accessories as are worn on a personal body. There have been limitations on the size of such commercial platinum products.
For these reasons, the present inventor has undertaken studies pertinent to a platinum electroforming method to solve the above-mentioned problems, i.e., the limitations on workability and size. Specifically, these studies have been directed to a method including the stages of forming by means of electrodeposition thick deposition layer of platinum on the surface of a mother die to which a release coat has been applied and releasing the deposited layer from the mother die to obtain an electroformed product of platinum having opposite convex and concave surfaces to those of the mother die. Adding to these stages, the method may include the stages of applying a release coat to the surface of the resultant electroformed product and treating by means of electrodeposition to obtain a product of platinum having the same convex and concave surfaces as those of the mother die. If the electroforming method may be materialized, it may simultaneously solve the problems such as the deficient workability and the limitation on size of platinum as aforementioned since it allows to conveniently prepare hollow products of platinum or products with a film of any thickness of platinum.
The limitations on workability and size are also solved by platinum electroforming on a mandrel. This method results in light weight, hollow articles, which are especially valuable in the field of jewelry making. There may be other applications as well.
2. Description of the Prior Art
From the above reasons, there has been a great demand for the electroforming of platinum. In fact, various studies on the electroforming of platinum have been conducted. However, no successful process has been completed so far. This is because a thickness of a deposited layer to be required in the electroforming is about 10-50 times as large as usual electroplating (for example, Japanese Patent Laid open Publication No. 107,794/1990). Specifically, one will fail to prepare the deposited layer of such a thickness because deposited platinum has a tendency to occlude hydrogen, which increases an internal stress of the deposited layer, resulting in generation of cracks (micro crevices). Thus, one cannot obtain the desirable deposited layer having sufficient strength and thickness to be used for commercial products. In particular, special consideration must be given to physical and mechanical properties of the deposited layer, since such layer per se becomes a product of electroforming. The generation of cracks may therefore cause fatal problems to the electroformed products.
In addition, a general platinum metal, which is not a deposited metal prepared by electroforming or electroplating, has a crystal structure of face centered cubic lattice. Also, it is soft (approximately 40 Hv) and ductile. However, ornaments, e.g., rings, necklaces made of platinum having these characteristics possess the drawbacks of being easily scratched and deformed because they are soft and abradable.
Because of these reasons, platinum is conventionally alloyed with other metals to increase hardness for manufacturing ornaments using platinum. This method, though it allows the hardness of the platinum alloy to increase, however, causes generation of intermetallic compounds in the platinum alloy to result in brittleness of the platinum alloy. This method also has the disadvantage of generation of an oxide film in the steps of heating or brazing a platinum alloy, thereby reducing the external quality of the platinum alloy. Accordingly, it is desirable to utilize means other than such alloying methods to improve the hardness of a platinum alloy.